In this paper, we apply the switched split vector quantiser (SSVQ) for coding short-term spectral envelope information in wideband speech coding to compare and contrast two LPC parameter representations: line spectral frequencies (LSFs) and immittance spectral pairs (ISPs). The SSVQ is the hybrid of a switch vector quantiser and split vector quantiser, which has been shown in previous studies to be more efficient, in terms of rate-distortion, as well as possessing lower computational complexity, than the split vector quantiser (SVQ). On the TIMIT database, the five-part SSVQ requires 43 and 44 bits/frame to transparently code LSFs and ISPs, respectively. This 1 bit/frame difference between LSFs and ISPs is also observed in five-part SVQ. The split-multistage vector quantiser (S-MSVQ) with MA predictor from the AMR-WB speech coder (ITU-T G.722.2) is also used as a basis of comparison where we find the SSVQ, which is a memoryless quantisation scheme, to be competitive at 46 bits/frame.